xx.] NEW ORDERS OF SPECTRA. 275 



element. Further, the continuous spectrum of -the solid ele- 

 ment is observed in the case of some well-known compounds, 

 whereas all known compounds are resolved by the high tension 

 spark into their constituents. We have a right to assume, 

 therefore, that an element in the solid state is a more complex 

 mass than the element in a state of vapour, since its spectrum 

 is the same as that of a mass known to be more complex. 

 Again, when changes occur in the spectrum of the same sub- 

 stance, they are always in the same direction; and, further, the 

 spectra we obtain from elements in a state of vapour are 

 similar in character to those we obtain from vapours of known 

 compounds. 



So far we have continuous, fluted, and line spectra, but this 

 is not all ; certain bodies, both simple and compound, when we 

 study them by their absorption at ordinaiy temperatures, give 

 us phenomena not included in the above statement. 



Here is what I said on this subject in 1874 l : 



" At ordinary temperatures in some cases, as in selenium, the 

 more refrangible end is absorbed : in others the continuous spec- 

 trum in the blue is accompanied by a continuous spectrum in the 

 red. On the application of heat, the spectrum in the red disappears, 

 that in the blue remains ; and, further, as Faraday has shown in 

 his researches on gold leaf, the masses which absorb in the blue 

 may be isolated from those which absorb in the red. It is well 

 known that many Rubstances known to be compounds, in solution 

 give us an absorption in the blue or blue and red ; and also that the 

 addition of a substance known to be a compound (such as water) to 

 substances known to be compounds which absorb the blue, super- 

 adds an absorption in the red. 



" In those cases which do not conform to what has been stated, 

 the limited range of the visible spectrum must be borne in mind. 

 Thus I have little doubt that the simple gases at the ordinary 

 conditions of temperature and pressure have an absorption in the 

 ultra-violet, and that highly compound vapours and liquids are often 



1 Proc. R. S. No. 153, 1874. 



T 2 



